1. Field of the Invention
This invention relates to a process for preparing textile fibers, especially nylon fibers, and more particularly concerns improving their whiteness by adding a phenyl phosphinate using an improved technique.
2. Background Art
In the conventional production of textile fibers of synthetic organic polymers, it is customary to add certain chemicals to the polymer for various purposes. Among such additives are pigments, antioxidants, ultraviolet screeners, delusterants, antistatic agents, whiteners and the like. The addition of various phenyl phosphinate salts and combinations thereof to nylon polymers to inhibit yellowing of the resulting nylon yarns is known from the disclosures of several patents, such as U.S. Pat. Nos. 3,374,288 (Lange), 3,947,424 (Tomek), and 2,981,715 (Ben). Indeed, in the commercial production of some melt-spun nylon filaments, the agents added to the polymer have included sodium phenyl phosphinate and a hindered phenol, as antioxidants, titanium dioxide and polyethylene oxide. Such fibers have, nevertheless, been noted to yellow on exposure to heat and light. Attempts to solve this problem by the addition of more sodium phenyl phosphinate in the polymer sometimes causes problems. Sodium phenyl phosphinate is insoluble in molten nylon-66. Such insolubility can lead to the formation of spherulites in the yarn during melt spinning, which in turn can alter the luster of the yarn and give it a chalky appearance, as well as cause more weak spots in the yarn which can lead to more broken yarns.
Accordingly, there has still been a real need to prepare a fiber that has improved resistance to yellowing, without encountering additional problems.
Conventional production of textile fibers generally includes application of an oil or an aqueous finish to the surface of the fibers. The customary purposes of the finish are to protect the fibers from damage by subsequent contact with machinery and to improve antistatic and tactile properties of the fibers. In addition to water or oil as the main ingredient, such finishes customarily include various chemical compounds depending on the anticipated use of the fiber. Among typical finish ingredients are mixtures of surfactants, lubricants, emulsifiers, antioxidants, antistatic agents and the like.